In recent years, electric apparatuses have been controlled by an inverter circuit because of environmental protection movement, thereby saving energy, and pursuing higher efficiency. The vehicle industry, among others, has actively developed techniques related to environmental friendly technique, energy saving, and higher efficiency. These techniques put a hybrid vehicle (HEV) that is driven with either an electric motor or an engine, in the market.
An electric motor to be used in HEV is used with a high voltage, several hundreds volts, so that a capacitor to be used therein has electric characteristics, such as high withstanding voltage with low loss. A metalized film capacitor has therefore drawn attention. Since maintenance-free is demanded from the market, the metalized film capacitor that has a long service life has been increasingly employed in this application.
Metalized film capacitors can be separated almost into two groups: a first group employs an electrode made of metal foil; and a second group employs an electrode made of vapor deposited metal formed on dielectric film. The latter group using the electrode made of vapor deposited metal (hereinafter referred to as a vapor deposited metal electrode) has a smaller volume occupied by the electrode than other metalized film capacitors including the metal foil electrode. The latter group can have a small size a light weight. The vapor deposited metal electrode has a self-recovery function in which the vapor deposited metal electrode around a defective portion vaporizes and scatters, so that the capacitor can recover its function. This self-recovery function is generally called a self-healing property. Since the self-recovery function increases the reliability against dielectric breakdown, the metalized film capacitor has been widely employed. A thinner vapor deposited metal electrode invites greater amounts of vapor and scatter, namely the thinner electrode increases the self-healing properties, so that a higher withstanding voltage can be expected.
FIG. 21 is a sectional view of conventional metalized film capacitor 501. FIG. 22 is a plan view of a pair of metalized films of metalized film capacitor 501. Vapor deposited metal electrodes 501a and 501b are formed by vapor-depositing aluminum on one surfaces of dielectric films 502a and 502b made of, e.g. polypropylene except insulating margins 503A and 503B on one ends of dielectric films 502a and 502b, respectively. Zinc is thermally sprayed on other ends of dielectric films 502a and 502b opposite to the one ends, thereby forming sprayed-metal electrodes 504a and 504b. Vapor deposited metal electrodes 501a and 501b are connected to sprayed-metal electrodes 504a and 504b, respectively so that the electrodes can be drawn to the outside.
Vapor deposited metal electrodes 501a and 501b has non-vapor-deposited slits 505a and 505b having no vapor deposited metal electrode thereon made by transferring oil. Electrode 501a is separated into plural electrode segments 506a by slits 505a so that electrodes 506a extend to insulating margin 503a from a center of width W of a center region (effective electrode section) which constitutes a capacitance. Vapor deposited metal electrode 501a is located at an area extending from the center of width W of the effective electrode section toward sprayed-metal electrode 504a, i.e. opposite to insulating margin 503a. Plural electrode segments 506a are connected in parallel to vapor deposited metal electrode 501a with fuses 507a. Electrode 501b is separated into plural electrode segments 506b by slit 505b so that electrodes 506b extend to insulating margin 503b from the center of width W of the center region (effective electrode section) which constitutes a capacitance. Vapor deposited metal electrode 501b is located at an area extending from the center of width W of the effective electrode section toward sprayed-metal electrode 504b, i.e. opposite to insulating margin 503b. Plural electrode segments 506b are connected in parallel to vapor deposited metal electrode 501b with fuses 507b. 
Electrode 501a includes low resistance section 508a which is thick locally at an end of electrode 501a contacting sprayed-metal electrode 504a. This structure reduces a connection resistance. Electrode 501b includes low resistance section 508b which is thick locally at an end of electrode 501b contacting sprayed-metal electrode 504b. This structure reduces a connection resistance. After electrodes 501a and 501b are formed, low resistance sections 508a and 508b can be formed by vapor-depositing aluminum or zinc only onto the ends of electrodes 501a and 501b. 
Zinc can reduce a melting point of the low resistance section, and hence, increase the adhesion between electrodes 501a and 501b and sprayed-metal electrodes 504a and 504b, accordingly providing metalized film capacitor 501 with a low resistance and high reliability.
Patent Literatures 1-3 disclose conventional metalized film capacitors similar to capacitor 501.
Since the vapor deposited metal electrode is very thin, the vapor deposited metal electrode can be oxidized and deteriorate due to water. An outer package made of resin prevents the water from entering in order to provide humidity resistance.
In recent years, the market demands a metalized film capacitor having a small size, accordingly requiring a thin outer package. The metalized film capacitor mounted particularly into a vehicle is often subjected to harsh environment, e.g. high temperature, high humidity, depending on the mounted locations. Maintaining the high withstanding voltage will entail a thinner vapor-deposited film, accordingly requiring a large humidity resistance.
Conventional metalized film capacitor 501 has the self-healing properties, and reduces heat generation due to fuses 507a and 507b. In other words, a larger current flows in metalized film capacitors 501a and 501b closer to sprayed-metal electrodes 504a and 504b, and a smaller current flows therein farther away from electrodes 504a and 504b. Fuses 507a and 507b, and electrode segments 506a and 506b are disposed closer to insulating margins 503a and 503b toward which the electric current becomes smaller. The heat generated by a current flowing in fuses 507a and 507b can be thus reduced, thereby preventing the temperature rise.
To improve the humidity resistance of metalized film capacitor 501, an alloy can be used as the vapor deposited metal electrode. To be more specific, an alloy made of plural metals, e.g. aluminum, zinc, and magnesium, is used as the electrode for improving the humidity resistance of capacitor 501. For instance, an alloy-electrode mainly made of aluminum with magnesium added thereto reduces water in the film or on the surface of the film due to the reaction shown in formula 1, thereby improving the humidity resistance.Mg+2H2O→Mg(OH)2+H2  (1)
The electrode made of the alloy thus reduces water that causes leakage current, thereby improving the characteristics of metalized film capacitor 501.
However, it is difficult for metalized film capacitor 501 mounted in a vehicle to obtain enough humidity resistance to the harsh environment although capacitor 501 employs the alloy-electrode.
As metalized film capacitor 501 has a small size, metalized film capacitor 501 entails a thinner film, which causes a lower withstanding voltage accordingly.